1. Field of the Invention
The present invention relates to the effect of changes in Young's modulus with temperature, and in particular, the effect of temperature on Young's modulus of Nb/Nb.sub.3 Sn bi-metallic strips.
2. Discussion of the Relevant Art
The use of bi-metallic strips as temperature sensing devices has been known in the temperature measuring art for many years. Most of these bi-layered strips depend for their operation upon the change in the radius of curvature of the strips during temperature changes by virtue of a difference in the coefficient of expansion of the two components, usually two metals of said strips. Heretofore, it has not been known to utilize temperature dependent changes in the Young's modulus of one of the components of the bi-layer strip for temperature sensing purposes.
Certain transition metal/metal or metalloid alloy bi-layer combinations have been used during low temperature work as super conducting materials, principally by virtue of the super-conducting qualities of the crystals of the transition metal/metal or metalloid alloy. Of a particular interest in this group of compounds have been niobium stannide layers, in particular, niobium stannide on niobium layers.
These super-conductive materials are usually either layered on other materials, for example, on copper, steel or aluminum as disclosed in U.S. Pat. No. 3,537,827 to Benz or have been coated upon other materials such as a barium ferrite slurry as disclosed in U.S. Pat. No. 3,534,459 to Kudo et al.
There have been studies of Young's modulus of niobium stannide both as single crystals, (Keller and Hanak: Phys. Rev. 154,628; 1967) and as polycrystals (Testardi, Physical Acoustics, Mason & Thurston Eds. Vol. X, p193 and Vol. XIII p29, 1977 Academic Press, New York). On the basis of the temperature dependence of the elastic moduli revealed by the single crystal work, applicants herein believed that the polycrystal work, carried out by ultrasonic measurement, was not representative of the true variation with temperature of the Young's modulus of niobium stannide in the temperature range 4-300 K. Applicants herein noted that niobium stannide and niobium have substantially identical coefficients of thermal expansion. Therefore, since Young's modulus of niobium itself is well known, they determined to study Young's modulus of niobium stannide by preparing an internally stressed bimetallic composite of a niobium stannide layer upon niobium film, and thus determine the variation with temperature of Young's modulus of niobium stannide from temperature dependent changes in the radius of curvature of the bimetallic strip.